Spring源码解析（七）——生命周期——BeanPostProcessor

https://blog.csdn.net/u011734144/article/details/72600932

http://www.cnblogs.com/lucas2/p/9430169.html

 

BeanPostProcessor：bean的后置处理器。在bean初始化前后进行一些处理工作。

public interface BeanPostProcessor {

	/**
	 * Apply this BeanPostProcessor to the given new bean instance before any bean
	 * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
	 * or a custom init-method). The bean will already be populated with property values.
	 * The returned bean instance may be a wrapper around the original.
	 * @param bean the new bean instance
	 * @param beanName the name of the bean
	 * @return the bean instance to use, either the original or a wrapped one;
	 * if {@code null}, no subsequent BeanPostProcessors will be invoked
	 * @throws org.springframework.beans.BeansException in case of errors
	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
	 * 初始化之前工作
	 */
	Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;

	/**
	 * Apply this BeanPostProcessor to the given new bean instance after any bean
	 * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
	 * or a custom init-method). The bean will already be populated with property values.
	 * The returned bean instance may be a wrapper around the original.
	 * 
In case of a FactoryBean, this callback will be invoked for both the FactoryBean
	 * instance and the objects created by the FactoryBean (as of Spring 2.0). The
	 * post-processor can decide whether to apply to either the FactoryBean or created
	 * objects or both through corresponding {@code bean instanceof FactoryBean} checks.
	 * 
This callback will also be invoked after a short-circuiting triggered by a
	 * {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
	 * in contrast to all other BeanPostProcessor callbacks.
	 * @param bean the new bean instance
	 * @param beanName the name of the bean
	 * @return the bean instance to use, either the original or a wrapped one;
	 * if {@code null}, no subsequent BeanPostProcessors will be invoked
	 * @throws org.springframework.beans.BeansException in case of errors
	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
	 * @see org.springframework.beans.factory.FactoryBean
	 * 初始化之后工作
	 */
	Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;

}

例子

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;

/**
 * 后置处理器：初始化前后进行处理工作
 * 将后置处理器加入到容器中
 * @author lfy
 */
@Component
public class MyBeanPostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("postProcessBeforeInitialization..."+beanName+"=>"+bean);
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("postProcessAfterInitialization..."+beanName+"=>"+bean);
        return bean;
    }
}

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

//@Component
public class Car implements InitializingBean, DisposableBean {

    private String name;

    public Car(String name) {
        this.name = name;
        System.out.println("car constructor...");
    }

    public void initMethod() {
        System.out.println("car name: " + name);
        System.out.println("car ... initMethod...");
    }

    public void destoryMethod() {
        System.out.println("car ... destoryMethod...");
    }

    @Override
    public void destroy() throws Exception {
        System.out.println("car ...DisposableBean... destory");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("car...InitializingBean...afterPropertiesSet");
    }

    @PostConstruct
    public void postConstruct() {
        System.out.println("car...postConstruct");
    }

    @PreDestroy
    public void preDestory() {
        System.out.println("car...preDestory");
    }
}

import com.atguigu.bean.Car;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

/**
 * bean的生命周期：
 * 		bean创建---初始化----销毁的过程
 * 容器管理bean的生命周期；
 * 我们可以自定义初始化和销毁方法；容器在bean进行到当前生命周期的时候来调用我们自定义的初始化和销毁方法
 *
 * 构造（对象创建）
 * 		单实例：在容器启动的时候创建对象
 * 		多实例：在每次获取的时候创建对象\
 *
 * BeanPostProcessor.postProcessBeforeInitialization
 * 初始化：
 * 		对象创建完成，并赋值好，调用初始化方法。。。
 * BeanPostProcessor.postProcessAfterInitialization
 * 销毁：
 * 		单实例：容器关闭的时候
 * 		多实例：容器不会管理这个bean；容器不会调用销毁方法；
 *
 *
 * 遍历得到容器中所有的BeanPostProcessor；挨个执行beforeInitialization，
 * 一但返回null，跳出for循环，不会执行后面的BeanPostProcessor.postProcessorsBeforeInitialization
 *
 * BeanPostProcessor原理
 * populateBean(beanName, mbd, instanceWrapper);给bean进行属性赋值
 * initializeBean
 * {
 * applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
 * invokeInitMethods(beanName, wrappedBean, mbd);执行自定义初始化
 * applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
 *}
 *
 *
 *
 * 1）、指定初始化和销毁方法；
 * 		通过@Bean指定init-method和destroy-method；
 * 2）、通过让Bean实现InitializingBean（定义初始化逻辑），
 * 				DisposableBean（定义销毁逻辑）;
 * 3）、可以使用JSR250；
 * 		@PostConstruct：在bean创建完成并且属性赋值完成；来执行初始化方法
 * 		@PreDestroy：在容器销毁bean之前通知我们进行清理工作
 * 4）、BeanPostProcessor【interface】：bean的后置处理器；
 * 		在bean初始化前后进行一些处理工作；
 * 		postProcessBeforeInitialization:在初始化之前工作
 * 		postProcessAfterInitialization:在初始化之后工作
 *
 * Spring底层对 BeanPostProcessor 的使用；
 * 		bean赋值，注入其他组件，@Autowired，生命周期注解功能，@Async,xxx BeanPostProcessor;
 *
 * @author lfy
 *
 */
@ComponentScan("com.atguigu.bean")
@Configuration
public class MainConfigOfLifeCycle {

    @Bean(initMethod="initMethod",destroyMethod="destoryMethod")
    public Car car(){
        return new Car("audi");
    }
}

import com.atguigu.config.MainConfigOfLifeCycle;
import org.junit.Test;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class IOCTest_LifeCycle {

    @Test
    public void test01(){
        //1、创建ioc容器
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfigOfLifeCycle.class);
        System.out.println("容器创建完毕");

        //关闭容器
        applicationContext.close();
    }
}

运行结果

从结果可以看出，spring管理的bean，会先执行postProcessBeforeInitialization，然后再执行初始化方法，如：@PostConstruct > InitializingBean > init-method

初始化：对象创建完成，并赋值好，调用初始化方法（@PostConstruct > InitializingBean > init-method）

初始化之前，调用BeanPostProcessor.postProcessBeforeInitialization

初始化之后，调用BeanPostProcessor.postProcessAfterInitialization

 

跟踪源码：

AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfigOfLifeCycle.class)=>

refresh();=>
finishBeanFactoryInitialization(beanFactory);=>

beanFactory.setConversionService(
                    beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));=>

doGetBean(name, requiredType, null, false);=>

sharedInstance = getSingleton=>

return createBean(beanName, mbd, args);=>

Object beanInstance = doCreateBean(beanName, mbdToUse, args);=>

populateBean先为属性赋值，然后initializeBean

applyBeanPostProcessorsBeforeInitialization方法，遍历得到容器中所有的BeanPostProcessor，挨个执行beforeInitialization。一旦返回null，跳出for循环，不会执行后面的beanProcessor.postProcessAfterInitialization。

小总结

 * BeanPostProcessor原理
 * populateBean(beanName, mbd, instanceWrapper);给bean进行属性赋值
 * initializeBean
 * {
 * applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
 * invokeInitMethods(beanName, wrappedBean, mbd);执行自定义初始化
 * applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
 *}